As a method for increasing the recording capacity of an optical disc, it is already known to minimize a laser spot by shortening the wavelength of a laser beam for conducting recording/reproducing of data and by increasing NA of an objective lens for recording/reproducing of data, or to multiple the recording layer into a plural number thereof. As such the multi-layer disc, a dual-layer disc is already put into practical use thereof, in the field of a DVD and a Blu-ray Disc (hereinafter, being described as “BD”). Also, in recent years, an optical disc having three (3) or more recording layers thereof is proposed, and for example in the following Non-Patent Document 1 is proposed a BD having six (6) recording layers.    [Non-Patent Document 1] ODS 2006 Technical digest (2006) 041 (pp 123-125)